This invention relates to additives for liquid hydrocarbons and to liquid hydrocarbon compositions containing the same. More particularly, this invention relates to additives for lubricating compositions and to lubricating compositions comprising the same.
As is well known, there are many instances, particularly under "Boundary Lubrication" conditions where two rubbing surfaces must be lubricated, or otherwise protected, so as to prevent wear and to ensure continued movement. Moreover, where, as in most cases, friction between the two surfaces will either increase the power required to effect the movement or reduce the recovery efficiency, where the movement is an integral part of an energy conversion system, it is most desirable to effect the lubrication in a manner which will minimize this friction. As is also well known, both wear and friction can be reduced, with various degrees of success, through the addition of a suitable additive or combination thereof, to a natural or synthetic lubricant. Similarly, continued movement can be insured, again with varying degrees of success, through the addition of one or more appropriate additives.
With respect to wear, several suitable additives have been proposed heretofore. In general, these additives function by forming a protective coating on the moving surfaces. Moreover, these additives are, generally, only slightly soluble in the base oil medium and are therefore, easily separated from the oil at the moving surfaces. Generally, the antiwear agent coating is maintained through physical, rather than chemical, bonding.
Extreme pressure agents also form a protective coating on the surface of the moving metal parts thereby preventing metal to metal contact even when the base lubricating oil is effectively squeezed from between the surfaces. These coatings are, however, generally effected through chemical bonding and are, therefore generally more stable than the coatings formed by antiwear agents. Metal dialkyldithiophosphates are, of course, included amongst the list of extreme pressure agents known to be effective in the prior art.
Similarly, antifriction agents or oiliness or lubricity agents as the same are often referred to in the prior art functioned by forming a coating on the surface of the moving metal parts. As in the case of antiwear agents, however, the coating bonds are generally, effected physically, rather then chemically, and the bonding between an antifriction agent and the surface is, generally weaker than the bond formed between an antiwear agent and the metal surface.
As is also well known in the prior art, and as is suggested by the foregoing, antiwear, antifriction and extreme pressure agents, as well as other agents, compete for the surface of the moving metal parts which are subjected to lubrication with a given composition and, indeed, extreme care must, generally, be exercised in the selection of these several agents to ensure compatibility and effectiveness. As is equally well known, several additives which are commonly used in lubricating compositions perform multiple function. As a result, several known compositions will contain more than one additive exhibiting antiwear properties, more than one additive exhibiting antifriction properties and more than one additive exhibiting extreme pressure properties.
Representative of the multifunctional additives are the metal dialkyl dithiophosphates which, among other things, exhibit antioxidant properties and antiwear properties. Of these compounds, the zinc dialkyldithiophosphates are most commonly used in lubricant compositions and, while zinc dialkyldithiophosphate affords excellent oxidation resistance and exhibits superior antiwear properties, the same appears to increase the friction between the moving surfaces. As a result, compositions containing zinc dialkyldithiophosphate as well as other metal dialkyldithiophosphates where the metal forms a relatively hard metal oxide do not offer the most desirable lubricity and, in turn, lead to significant energy losses in overcoming friction even when antifriction agents are included in the composition. Notwithstanding this, however, the zinc dialkyldithiophosphates continue to be used in lubricating compositions because of their good compatibility with other, conventional, additives and because of their antioxidation and antiwear characteristics. Such lubricant compositions do, then, generally, result in higher fuel consumption than is considered particularly desirable, especially in light of the current energy crisis.
In light of the foregoing, then, the need for an improved lubricating composition containing a zinc or similar metal dialkyldithiophosphate that will permit operation of moving parts under boundary conditions with reduced friction is believed to be readily apparent. Similarly, the need for such a composition that can be used without the loss of other desirable lubricant properties is also believed to be readily apparent.